This disclosure relates generally to Processes for the thermal reduction of sulfur dioxide to elemental sulfur. Sulfur dioxide is reduced in a single reaction furnace zone. The design of the reaction furnace includes an alumina monolith that performs as an active catalyst to reduce the residence time required in the reaction furnace and to enhance completion of the reduction reactions. The reaction furnace is followed by the Claus conversion zone, wherein residual H2S and SO2 are further reacted to produce additional elemental sulfur. Three methods to eliminate soot formation and two methods to consume produced H2 and CO are described. Wherein one or a combination of these methods could be employed which consists of a) adding steam (water vapor), b) adding recycled sulfur and c) adding recycled tail gas.